The embodiments described herein relate generally to power relays, and more specifically, to systems and methods for cleaning relay contacts.
An electric discharge, referred to herein as contact arcing, occurs between contacts within a mechanical power relay when a voltage and a current present at the contacts are above predefined levels and the contacts are switched between a closed position and an open position. Contact arcing occurs because the current in the circuit cannot instantaneously jump to zero when the relay is opened, and as a result, a transient arc forms across the separating contacts. An arc voltage is defined as a voltage that exists across contacts separated by a small gap that will cause an electric discharge across the gap. An arc current is defined as a current necessary to sustain an arc caused by the arc-voltage electric discharge. The arc voltage and arc current are known values associated with a specific relay and are dependent on the materials included in the relay contacts.
In traditional appliances that include induction motors, motor windings are switched through power relays to change the motor speed. Currents through these relays typically are higher than one amp. This level of electric current is above the predefined arc current for the relays and causes contact arcing when the relay is switched between closed and open positions.
Arcing can be beneficial as it removes sulfidation, oxidation, and/or contaminates from surfaces of the relay contacts. In relay applications where the voltage and/or current present at the contacts is less than the arc voltage and/or arc current, since contact arcing will not occur, a film of sulfidation, oxidation, and/or contaminates may form on the surfaces of the relay contacts to a level that negatively affects circuit continuity. Furthermore, the relay may malfunction due to corrosion over time.